The invention relates to a circuit for pre-charging an intermediate circuit and to an electrical system.
DE 10 2014 217 908 A1 discloses a circuit for pre-charging an intermediate circuit or an intermediate circuit capacitor. Circuits of this kind are provided, when the electrical system comprising the intermediate circuit is switched on, to initially pre-charge the intermediate circuit to a voltage close to an operating voltage of a high-voltage battery that feeds the intermediate circuit after the pre-charging. If such pre-charging were to be omitted, an impermissibly high charging current could flow when the high-voltage battery is connected to the intermediate circuit.
The invention is based on the object of providing a circuit for pre-charging an intermediate circuit and to an electrical system, which make it possible to pre-charge the intermediate circuit reliably.
The invention achieves this object by way of a circuit for pre-charging an intermediate circuit and an electrical system in accordance with embodiments of the invention.
The circuit is configured to pre-charge an intermediate circuit, in particular one or more intermediate circuit capacitors of the intermediate circuit, to a pre-charging voltage. The pre-charging voltage may depend on an operating voltage of an electrical energy store, for example in the form of a battery, which feeds the intermediate circuit after the pre-charging. The pre-charging voltage may, for example, be equal to the operating voltage or be lower than the operating voltage by a prescribed difference value (typically a few volts).
In addition to one or more intermediate circuit capacitors, the intermediate circuit has a positive branch and a negative branch. A positive intermediate circuit potential is typically present at the positive branch and a negative intermediate circuit potential is typically present at the negative branch.
The circuit for pre-charging an intermediate circuit has a first controllable energy source and a second controllable energy source. The first and the second energy source can change or suitably adjust an electrical energy or electrical power output at the respective output thereof in an actuation-dependent manner. The first energy source and the second energy source are looped in at their respective outputs in series between the positive branch and the negative branch.
The circuit for pre-charging an intermediate circuit also has an interference suppression unit, which is looped in between a connecting node of the output of the first energy source and of the output of the second energy source and a reference-ground potential, in particular PE (protective earth). The interference suppression unit is configured to reduce line-based and/or radiated interferences. The interference suppression unit can form or have a measurement impedance and have, for example, a resistor and a capacitor connected in parallel therewith.
The circuit for pre-charging an intermediate circuit also has a control device, for example in the form of a microprocessor or a digital signal processor. The control device is connected in a signal-transmitting manner to the first energy source and the second energy source and is configured to actuate the first energy source and the second energy source to generate an output signal pattern, for example in the form of an output voltage pattern, in such a way that said energy sources pre-charge the intermediate circuit.
In accordance with one embodiment, the first energy source is a voltage source, a current source or a combined voltage/current source. Accordingly, the second energy source may be a voltage source, a current source or a combined voltage/current source.
The first energy source and/or the second energy source can draw the energy from a low-voltage energy store or low-voltage generator in order to generate the respective output signal pattern or to pre-charge the intermediate circuit.
In accordance with one embodiment, the first energy source has a DC-isolating DC/DC converter, which is fed, for example, from a low-voltage supply system, for example from a battery. Accordingly, the second energy source can have a DC-isolating DC/DC converter, which is fed, for example, from the low-voltage supply system.
In accordance with one embodiment, the control device is configured to actuate the first energy source and the second energy source independently of one another.
In accordance with one embodiment, the circuit has a measurement device, which is configured to measure a voltage between a middle potential and a reference-ground potential, in particular PE, and/or to measure a voltage between a potential present at the positive branch and the reference-ground potential, in particular PE, and/or to measure a voltage between a potential present at the negative branch and the reference-ground potential, in particular PE, and/or to measure a voltage dropped at the interference suppression unit. The measurement device can furthermore be configured to measure currents within the circuit and/or within further components.
In accordance with one embodiment, the measurement device is configured to detect a malfunction of the first energy source and/or of the second energy source based on the measured voltages and/or currents and, in the event of a detected malfunction of one of the two energy sources, to activate the respectively fault-free energy source in order to pre-charge the intermediate circuit.
In accordance with one embodiment, the control device is configured to actuate the first energy source and the second energy source in alternation to generate the output voltage signal pattern as an output voltage test pattern. To this end, the control device can be configured, for example, during first time intervals, to actuate the first energy source to generate an output voltage and to deactivate the second energy source so that it does not generate an output voltage and, during second time intervals, to actuate the second energy source to generate an output voltage and to deactivate the first energy source so that it does not generate an output voltage. The first time intervals and the second time intervals then follow one another in alternation. The output voltage test pattern can also serve, for example, to check the correct functioning of the measurement device.
In accordance with one embodiment, the control device is configured to detect, during the generation of the output voltage test pattern, based on the voltage/current or voltages/currents measured by means of the measurement device, both symmetrical and asymmetrical insulation faults in the intermediate circuit, in particular to locate insulation faults by means of different switch-on conditions of the two energy sources.
The electrical system according to the invention has an above-described circuit for pre-charging an intermediate circuit.
The electrical system also has one or more intermediate circuit capacitors, which is/are looped in between the positive branch and the negative branch of the intermediate circuit.
The circuit for pre-charging an intermediate circuit is configured to charge the intermediate circuit capacitor or capacitors up to a prescribed pre-charging voltage, for example after the electrical system has been switched on. After the intermediate circuit capacitor has been charged up to the pre-charging voltage, the intermediate circuit can be coupled, for example, to a battery.
In accordance with one embodiment, the current converter has a number of actuatable electrical switching elements, for example in the form of semiconductor switches, such as FETs or IGBTs, for example, wherein the control device is configured to actuate the electrical switching elements. The measurement device is configured to measure currents and voltages of the current converter (and possibly also of the circuit itself) in different switch-on states of the first energy source and of the second energy source and in different switching states of the switching elements and to evaluate same in such a way that possible insulation faults in the entire electrical system can be detected and located.
The electrical system can also have an electrical energy store, in particular in the form of a battery, which is configured to supply electrical energy to the intermediate circuit after the pre-charging.